The main components of a drive train of a motor vehicle are a drive assembly and a transmission. The transmission converts torques and speeds, and thus transmits the traction force produced by the drive assembly. The present invention concerns a method for operating a drive train that comprises at least a transmission and, as the drive assembly, a hybrid drive with an internal combustion engine and an electric motor.
In a drive train with a so-termed parallel hybrid drive, a clutch is connected between the internal combustion engine and the electric motor of the hybrid drive, by means of which the internal combustion engine of the hybrid drive can be uncoupled from a drive output of the drive train. When such a drive train with a parallel hybrid drive is started, the internal combustion engine is typically switched off and the clutch connected between the internal combustion engine and the electric motor is disengaged.
When the switched-off internal combustion engine is to be started, it can be entrained into motion by the electric motor by at least partially engaging the clutch connected between the internal combustion engine and the electric motor, and to optimally carry out the entrainment of the not yet ignited internal combustion engine, at least the so-termed break-away torque and preferably also the so-termed friction torque of the internal combustion engine must be known. Until now these torques have been specified by the engine manufacturer and entrainment is then carried out on the basis of the specified torques.
However, this fails to take into account that the break-away and friction torques of the internal combustion engine can change over its operating life. This results in sub-optimal entrainment of the internal combustion engine.